Ink jet printing has become recognized as a prominent contender in the digitally controlled, electronic printing arena because of, e.g., its non-impact, low noise characteristics and system simplicity. For these reasons, ink jet printers have achieved commercial success for home and office use and other areas.
Traditionally, digitally controlled inkjet printing capability is accomplished by one of two technologies. Both technologies feed ink through channels formed in a printhead. Each channel includes a nozzle from which droplets of ink are selectively extruded and deposited upon a medium.
The first technology, commonly referred to as “drop-on-demand” ink jet printing, provides ink droplets for impact upon a recording surface using a pressurization actuator (thermal, piezoelectric, etc.). Selective activation of the actuator causes the formation and ejection of a flying ink droplet that crosses the space between the printhead and the print media and strikes the print media. The formation of printed images is achieved by controlling the individual formation of ink droplets, as is required to create the desired image. Typically, a slight negative pressure within each channel keeps the ink from inadvertently escaping through the nozzle, and also forms a slightly concave meniscus at the nozzle, thus helping to keep the nozzle clean.
Conventional “drop-on-demand” ink jet printers utilize a pressurization actuator to produce the ink jet droplet at orifices of a print head. Typically, one of two types of actuators is used including heat actuators and piezoelectric actuators. With heat actuators, a heater, placed at a convenient location, heats the ink causing a quantity of ink to phase change into a gaseous steam bubble that raises the internal ink pressure sufficiently for an ink droplet to be expelled. With piezoelectric actuators, an electric field is applied to a piezoelectric material possessing properties that create a mechanical stress in the material causing an ink droplet to be expelled. The most commonly produced piezoelectric materials are ceramics, such as lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate.
The second technology, commonly referred to as “continuous stream” or “continuous” ink jet printing, uses a pressurized ink source which produces a continuous stream of ink droplets. Conventional continuous ink jet printers utilize electrostatic charging devices that are placed close to the point where a filament of working fluid breaks into individual ink droplets. The ink droplets are electrically charged and then directed to an appropriate location by deflection electrodes having a large potential difference. When no print is desired, the ink droplets are deflected into an ink capturing mechanism (catcher, interceptor, gutter, etc.) and either recycled or disposed of. When a print is desired, the ink droplets are not deflected and allowed to strike a print media. Alternatively, deflected ink droplets may be allowed to strike the print media, while non-deflected ink droplets are collected in the ink capturing mechanism.
Regardless of the type of inkjet printer technology, it is desirable to keep the ink free of particles that may clog or partially clog the printhead nozzles. In inkjet printing, some micro-sized solid particles present in printing ink. These solid particles may come from dry ink in the system, or conglomeration of sub-micron ink pigments. There are also evidences of growth of bacteria that form particles in the ink. In other cases the origins of these solid particles are unknown. For the particles, which sizes are in microns, comparable to the nozzle size, may not pass through nozzles smoothly, causing droplet deflection that adversely affects droplet placement. The particles even can block the nozzles that end in printhead early replacement. The problem is known as a nozzle contamination issue in inkjet printing. To eliminate the contamination issue, a method to produce ultra clean ink is called for. Another problem related to particle contamination is that once a printhead is contaminated by the particles, it has to be dismounted and sent to manufacturer for refurbishing, which is expensive in both finance cost and production time.
It is important to point out that even though filters are commonly used in inkjet printhead to remove particles, they are not effective at removing in-situ particles that are formed near the printhead nozzles as dried ink or conglomerations of small particles. These in-situ particles tend to form within the printhead near the nozzles when the printhead is not in service. Furthermore, efforts of removing these particles by recycling the ink through the ink tank with filters are not fully successful since some particles are trapped in the areas where the flow field is dominated by local circulation near the nozzles. In the printing mode, however, these particles may randomly stray away from the local circulation and reach the nozzle, causing nozzle contamination. This issue is particularly severe for continuous inkjet printing where a large amount of ink is normally consumed during a printing operation.
U.S. Pat. No. 7,150,512 discloses a device using a solvent based cleaning fluid to flush the nozzle, drop generator and catcher while the continuous ink jet printing device is not in print mode. The reclaimed ink from the catcher has less debris therefore the recycling rate to deliver the ink is increased due to a lower concentration of debris being present in the reclaimed ink thereby minimizing clogging of the components.
U.S. Pat. No. 6,964,470 discloses a method to prevent adhesion of colorant particles to the tip of an ink guide (or nozzle). When in cleaning mode a piezoelectric device vibrates the ink guide, thereby giving the colorant particles kinetic energy to eject from the surface.
U.S. Pat. No. 5,543,827 discloses an ink jet printhead nozzle when in cleaning mode a piezoelectric device vibrates the nozzle plate to facilitate cleaning solvent to flow in the same direction as gravity. A controller operates not only the valve to allow cleaning fluid to flow but also controls the nozzle plate vibration.
These techniques are not always effective especially when trying to remove particles that are trapped in areas where the fluid flow field is dominated by local circulation, for example, near the nozzle of a printhead. Therefore, it would be useful to have an apparatus and method capable of removing these particles.